The present invention relates to a device for illuminating an original document or image (hereinafter referred to as an "original") for a copying machine or the like, having an image forming optical system such as a "selfoc" lens which has a small image formation width.
In a conventional original illuminating device for an electronic copying machine or the like, as shown in FIGS. 1 and 2, a main reflector b and an auxiliary reflector c (FIG. 1) or an opposed reflector d (FIG. 2) are provided about a light source 1 at positions such that light from the light source a is condensed on an original mounted on a platen g. The configuration produces a lens image formation width f for an image forming optical system e, which may, for instance, be a "selfoc" lens. However, these conventional configurations are accompanied by a rather serious drawback in that, when the lens image formation width f is reduced, for instance, to 5 mm or less, an unwanted shadow will be present if the original starts to "float" over the platen; that is, to separate from the platen. In order to eliminate this effect produced by floatation of the original, prior art illumination systems have been proposed which provide an increased light condensation width, in excess of that required for a normal copying operation. However, this increased condensation width is accompanied by a great reduction in the overall illumination efficiency, as shown by the dashed line graph of FIG. 3.